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  <title>Problems of Existing Work</title>
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<h1 style="direction:ltr;"><b><font color="#808000">Problems of Existing Work</b></font></h1>
<ul><li style="direction:ltr;"><h2>Hard to deploy</h2></li>
<ul><li style="direction:ltr;">TCP variants and XCP</li>
<li style="direction:ltr;">Need modifications in OS kernel and/or routers</li>
</ul><li style="direction:ltr;"><h2>Cannot be used in shared networks</h2></li>
<ul><li style="direction:ltr;">Most reliable UDP-based protocols</li>
</ul><li style="direction:ltr;"><h2>Poor fairness</h2></li>
<ul><li style="direction:ltr;">Intra-protocol fairness</li>
<li style="direction:ltr;">RTT fairness</li>
</ul><li style="direction:ltr;"><h2>Manual parameter tuning</h2></li>
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<h3>Notes:</h3>
<p style="direction:ltr;"><font color="#000000">Even though there are a number of  new protocols, the basic problem has not been completely resolved yet.</font></p>
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<p style="direction:ltr;"><font color="#000000">I have mentioned that TCP variants and XCP are hard to deploy and therefore it is difficult to use them in real world applications.</font></p>
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<p style="direction:ltr;"><font color="#000000">Meanwhile, most of the reliable UDP-based protocols were only designed for private links, so the only purpose of their congestion control algorithms is to make use of as much bandwidth as possible.</font></p>
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<p style="direction:ltr;"><font color="#000000">In addition, many of these protocols need to manually tune the parameters per network situation, which is not practical in many cases.</font></p>
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